1. Field of the Invention
The present invention relates to a music reproducing apparatus.
2. Description of the Related Art
A music reproducing program that allows a smartphone or a tablet PC to function as a music reproducing apparatus is present. The music reproducing program allows the smartphone to reproduce music from a speaker of the smartphone and to output digital audio data from the smartphone to an external USB DAC (D/A converter). Conventionally, as digital audio data, PCM data (first digital audio data) that is encoded by PCM (Pulse Code Modulation) system in which sampling frequency is 44.1 kHz and the number of quantum bits is 16 bits is main stream. In recent years, there has been DSD data (second digital audio data) that is encoded by a 1-bit DSD (Direct Stream Digital) system in which a sampling frequency is 2.8224 MHz (=44.1 kHz×64) as digital audio data.
When the music reproducing program allows the smartphone to output DSD data from the smartphone to the USB DAC, the music reproducing program occasionally allows the smartphone to output the DSD data from the smartphone to the USB DAC via USB using frames of PCM data. This system is called DoP (DSD Audio over PCM Frames). For example, a USB audio class supports PCM data, but does not support DSD data. For this reason, when the smartphone and the USB DAC execute communication that supports the USB audio class, DSD data is output from the smartphone to the USB DAC by DoP.
FIG. 6 is a diagram illustrating DSD data that is stored in frames of PCM data. The frames of PCM data is configured by 24 bits. DSD data is stored in 16 bits of 24 bits. A marker that includes information representing that it is DSD data is stored in 8 bits of 24 bits. The USB DAC can judge that the digital audio data that is output is DSD data by the marker.
FIG. 7 is a diagram illustrating a concept of DoP output. The smartphone outputs DSD data to channel for PCM data of L channel of the USB DAC and to channel for PCM data of R channel of the USB DAC by DoP. In DoP output, DSD data is output from the smartphone to the USB DAC while DSD data is made look like PCM data. For this reason, noises are generated at time of switching from output of PCM data to output of DSD data (DoP output) or from output of DSD data to output of PCM data. To repress noises, the music reproducing program is designed so that the switching from output of PCM data to output of DSD data (DoP output) or from output of DSD data to output of PCM data is not executed as much as possible.
In the conventional music reproducing apparatus, when DSD data is output from the smartphone to the USB DAC (DoP output), stopping instruction of outputting (for example, so-called “pause”) from a user is accepted and the music reproducing apparatus allows the smartphone to stop the USB DAC (pausing process). At this time, as illustrating in FIG. 8, a device driver occasionally inserts PCM data automatically. For this reason, switching from output of DSD data (DoP output) to output of PCM data occurs and noises are generated from the USB DAC.